1. Field of the Invention
This invention relates to a dental shade guide for matching the color of a dental material with a particular tooth.
2. Description of the Related Art
Dental restorations repair weakened, damaged or missing teeth. Direct placement restorations are made by applying a dental composite directly to damaged tooth structure. Indirect placement restorations, including inlays and onlays, are also often made of dental composites but are shaped outside of the oral cavity and then placed in or on the tooth structure. Restorations may also include crowns, bridges, implants, dentures and the like that comprise an artificial tooth or set of teeth which is secured in place in the oral cavity.
Preferably, dental restorations simulate as close as possible the appearance of remaining visible tooth structure in the patient's mouth so that the restoration looks as natural as possible. However, the color of teeth varies from individual to individual, and also varies somewhat from tooth to tooth in the mouth. As such, care must be undertaken to select a restorative material that has a color which is closely similar to the color of adjacent teeth.
Typically, a set of dental shade guides, each of a different color, is used to select a color for the restoration. The shade guides are held next to the teeth in order to facilitate comparison of the colors of the different guides with the color of tooth structure adjacent the restoration. Once a particular guide is chosen, indicia on the guide enable the dentist to choose restorative material with proper coloring or pigments so that the restoration, once completed and in the mouth, appears as aesthetic as practicable.
The nature and perception of color is somewhat subjective. Color may be measured by a visual technique, often called the Munsell Color System, which identifies three parameters: hue, value and chroma. Hue is measured on a numeric scale for each of the ten color families (such as red, yellow-red, yellow and the like). Value (or brightness) varies from black to white on a numeric scale and the value of a given color can be modified by the addition of a white pigment. Chroma (or saturation) is a measurement of the amount of color which is present at a given hue, and ranges on a numeric scale from 0 (which is achromatic or gray and has no color) to a fully saturated hue which is 18. The hue, chroma and value taken together define the color of an object under specified lighting conditions.
The perceived color of an object may be modified by the translucency or opacity of the object. Opacity is often measured in terms of a contrast ratio, which changes in a particular object in accordance with the thickness of the object. For more information, see, e.g., "Restorative Dental Materials", edited by Robert G. Craig and published in 1989 by C. V. Mosby Company of St. Louis, Miss.
To date, a variety of dental shade guides have been commercialized. One widely available guide is in the shape of an elongated, integrally molded bar which varies in thickness in stepped regions along the length of the bar. The bar is slightly translucent, and as a result the stepped regions vary in opacity even though the color of the material is the same throughout the bar. In this manner, an attempt can be made to match the color of the shade guide with the color of the teeth while also considering the opacity of differing regions of the shade guide and the teeth.
Other types of shade guides are molded in the shape of a tooth, and have a depending handle for holding the guide next to the patient's teeth. The handle is opaque or transparent and made of a material which is different in composition and color from the tooth-shaped portion. The tooth-shaped portion, being made of slightly translucent material, varies in opacity from thinner areas of the tooth to thicker tooth areas, although the color of the material remains the same throughout the tooth. Some dentists prefer to use the tooth-shaped shade guide, apparently because the lighting conditions and variations in opacity through the tooth-shaped guide resemble the same phenomena in natural teeth.
The selection of a proper color for dental restorations, however, is an art that is sometimes difficult for certain individuals to master. Moreover, the time and expense of making restorations discourages additional attempts to match colors if the color of the first restoration does not appear realistic in the mouth. Consequently, there is a continuing need for a dental shade guide which facilitates selection of the proper color.